Glycemic responses to strenuous training in male professional cyclists with type 1 diabetes: a prospective observational study

Effects of 12-week combined interval running and resistance training on cardiac structure and performance in patients with type 1 diabetes

Background

Exercise has been suggested to effectively improve cardiac performance in children with type 1 diabetes (T1D) by enhancing the glycemic control. The purpose of this study was to investigate (1) effects of a 12-week combined interval running and resistance training (CIRRT) and (2) 1 month of detraining on cardiac structure and myocardial performance in adolescent males with T1D.

Methods

A total of 72 participants, including 48 adolescent males with T1D (fasting blood glucose (FBG): 274.67 ± 52.99 mg/dL, age: 15.20 ± 1.78 years) and 24 healthy adolescents (FBG: 90.75 ± 5.47 mg/dL, age: 15.08 ± 1.67 years), were recruited to the study. Participants were allocated into diabetes exercise (DE), diabetes control (DC), and healthy controls (HC) groups. The DE group performed 12 weeks of a CIRRT program three times per week. Blood glucose profile, echocardiography (ECHO) indices, and peak oxygen consumption (VO2peak) were measured pre- and post-intervention and following 1-month detraining period. Repeated measures ANOVA was used for pre- and post-intervention comparisons within the DE group and across the three study groups. Significance level was set at p < 0.05.

Results

Exercise intervention resulted in decreased hemoglobin A1c (HbA1c% = Pre: 10.44 ± 2.03, Post: 9.38 ± 1.66, p < 0.05), FBG, left ventricular (LV) internal diameter, and both tricuspid and mitral deceleration time (DT) in the DE group. VO2peak, ejection fraction (EF% = Pre: 62.38 ± 1.6, Post: 64.08 ± 1.18, p < 0.05), fractional shortening, early tricuspid diastolic inflow E velocity, and tricuspid velocity during atrial contraction were also increased following the exercise training. HbA1c (Pre vs Follow-up: 9.83 ± 1.73, p < 0.05), EF (Pre vs Follow-up: 62.97 ± 1.56, p < 0.05), LV, and DT tricuspid remained significantly improved after detraining period compared to the baseline. In the baseline, the glycemic index and ECHO variable significantly differed in the DE and DC groups with the HC group (p < 0.05). However, after the intervention, the DC and HC groups did not change significantly (p > 0.05).

Conclusion

The CIRRT intervention was associated with improved cardiac structure and performance in male adolescents with T1D potentially due to exercise-induced adaptations. Meanwhile, the results indicate that most cardiac morphological and functional changes are reversible following periods of inactivity in patients with T1D.

Applying technologies to simplify strategies for exercise in type 1 diabetes

Challenges and fears related to managing glucose levels around planned and spontaneous exercise affect outcomes and quality of life in people living with type 1 diabetes. Advances in technology, including continuous glucose monitoring, open-loop insulin pump therapy and hybrid closed-loop (HCL) systems for exercise management in type 1 diabetes, address some of these challenges. In this review, three research or clinical experts, each living with type 1 diabetes, leverage published literature and clinical and personal experiences to translate research findings into simplified, patient-centred strategies. With an understanding of limitations in insulin pharmacokinetics, variable intra-individual responses to aerobic and anaerobic exercise, and the features of the technologies, six steps are proposed to guide clinicians in efficiently communicating simplified actions more effectively to individuals with type 1 diabetes. Fundamentally, the six steps centre on two aspects. First, regardless of insulin therapy type, and especially needed for spontaneous exercise, we provide an estimate of glucose disposal into active muscle meant to be consumed as extra carbohydrates for exercise ('ExCarbs'; a common example is 0.5 g/kg body mass per hour for adults and 1.0 g/kg body mass per hour for youth). Second, for planned exercise using open-loop pump therapy or HCL systems, we additionally recommend pre-emptive basal insulin reduction or using HCL exercise modes initiated 90 min (1-2 h) before the start of exercise until the end of exercise. Modifications for aerobic- and anaerobic-type exercise are discussed. The burden of pre-emptive basal insulin reductions and consumption of ExCarbs are the limitations of HCL systems, which may be overcome by future innovations but are unquestionably required for currently available systems.

The Acute Effects of Real-World Physical Activity on Glycemia in Adolescents With Type 1 Diabetes: The Type 1 Diabetes Exercise Initiative Pediatric (T1DEXIP) Study

OBJECTIVE

Data from the Type 1 Diabetes Exercise Initiative Pediatric (T1DEXIP) study were evaluated to understand glucose changes during activity and identify factors that may influence changes.

RESEARCH DESIGN AND METHODS

In this real-world observational study, adolescents with type 1 diabetes self-reported physical activity, food intake, and insulin dosing (multiple-daily injection users) using a smartphone application. Heart rate and continuous glucose monitoring data were collected, as well as pump data downloads.

RESULTS

Two hundred fifty-one adolescents (age 14 ± 2 years [mean ± SD]; HbA1c 7.1 ± 1.3% [54 ± 14.2 mmol/mol]; 42% female) logged 3,738 activities over ∼10 days of observation. Preactivity glucose was 163 ± 66 mg/dL (9.1 ± 3.7 mmol/L), dropping to 148 ± 66 mg/dL (8.2 ± 3.7 mmol/L) by end of activity; median duration of activity was 40 min (20, 75 [interquartile range]) with a mean and peak heart rate of 109 ± 16 bpm and 130 ± 21 bpm. Drops in glucose were greater in those with lower baseline HbA1c levels (P = 0.002), shorter disease duration (P = 0.02), less hypoglycemia fear (P = 0.04), and a lower BMI (P = 0.05). Event-level predictors of greater drops in glucose included self-classified "noncompetitive" activities, insulin on board >0.05 units/kg body mass, glucose already dropping prior to the activity, preactivity glucose >150 mg/dL (>8.3 mmol/L) and time 70-180 mg/dL >70% in the 24 h before the activity (all P < 0.001).

CONCLUSIONS

Participant-level and activity event-level factors can help predict the magnitude of drop in glucose during real-world physical activity in youth with type 1 diabetes. A better appreciation of these factors may improve decision support tools and self-management strategies to reduce activity-induced dysglycemia in active adolescents living with the disease.

Exercise in adults with type 1 diabetes mellitus

Regular physical activity improves cardiometabolic and musculoskeletal health, helps with weight management, improves cognitive and psychosocial functioning, and is associated with reduced mortality related to cancer and diabetes mellitus. However, turnover rates of glucose in the blood increase dramatically during exercise, which often results in either hypoglycaemia or hyperglycaemia as well as increased glycaemic variability in individuals with type 1 diabetes mellitus (T1DM). A complex neuroendocrine response to an acute exercise session helps to maintain circulating levels of glucose in a fairly tight range in healthy individuals, while several abnormal physiological processes and limitations of insulin therapy limit the capacity of people with T1DM to exercise in a normoglycaemic state. Knowledge of the acute and chronic effects of exercise and regular physical activity is critical for the formulation of clinical strategies for the management of insulin and nutrition for active patients with T1DM. Emerging diabetes-related technologies, such as continuous glucose monitors, automated insulin delivery systems and the administration of solubilized glucagon, are demonstrating efficacy for preserving glucose homeostasis during and after exercise in this population of patients. This Review highlights the beneficial effects of regular exercise and details the complex endocrine and metabolic responses to different types of exercise for adults with T1DM. An overview of basic clinical strategies for the preservation of glucose homeostasis using emerging technologies is also provided.

Domesticating the condition: Design lessons gained from a marathon on how to cope with barriers imposed by type 1 diabetes

Through analytical autoethnographic analysis of marathon preparation, this study examines challenges faced by people with Type 1 Diabetes (T1D) who engage in high-performance sports. Autoethnographer and second-person perspectives (T1D runners, family members, and health providers) were collected through introspective activities (autoethnographic diary and in-depth interviews) to understand the T1D runner's coping experience. Six insights involved in T1D self-management were identified and analyzed with reference to related design tools (prototyping, archetyping and journey mapping). Finally, we conclude with a discussion of how endurance physical activity (PA) such as running helps to "domesticate" T1D, a term coined to reflect the difficulties that T1D presents for PA accomplishment and how T1D runners' experiences give them an opportunity to overcome PA barriers promoting physical culture and enriching further health psychology studies.

Association of HbA1c with VO2max in Individuals with Type 1 Diabetes: A Systematic Review and Meta-Analysis

The aim of this systematic review and meta-analysis was to evaluate the association between glycemic control (HbA1c) and functional capacity (VO2max) in individuals with type 1 diabetes (T1DM). A systematic literature search was conducted in EMBASE, PubMed, Cochrane Central Register of Controlled Trials, and ISI Web of Knowledge for publications from January 1950 until July 2020. Randomized and observational controlled trials with a minimum number of three participants were included if cardio-pulmonary exercise tests to determine VO2max and HbA1c measurement has been performed. Pooled mean values were estimated for VO2max and HbA1c and weighted Pearson correlation and meta-regression were performed to assess the association between these parameters. We included 187 studies with a total of 3278 individuals with T1DM. The pooled mean HbA1c value was 8.1% (95%CI; 7.9−8.3%), and relative VO2max was 38.5 mL/min/kg (37.3−39.6). The pooled mean VO2max was significantly lower (36.9 vs. 40.7, p = 0.001) in studies reporting a mean HbA1c > 7.5% compared to studies with a mean HbA1c ≤ 7.5%. Weighted Pearson correlation coefficient was r = −0.19 (p < 0.001) between VO2max and HbA1c. Meta-regression adjusted for age and sex showed a significant decrease of −0.94 mL/min/kg in VO2max per HbA1c increase of 1% (p = 0.024). In conclusion, we were able to determine a statistically significant correlation between HbA1c and VO2max in individuals with T1DM. However, as the correlation was only weak, the association of HbA1c and VO2max might not be of clinical relevance in individuals with T1DM.

A Brief Review on the Evolution of Technology in Exercise and Sport in Type 1 Diabetes: Past, Present, and Future

One hundred years ago, insulin was first used to successfully lower blood glucose levels in young people living with what was then called juvenile diabetes. While insulin was not a cure for diabetes, it allowed individuals to resume a near normal life and have some freedom to eat more liberally and gain the strength they needed to live a more active lifestyle. Since then, a number of therapeutic and technical advances have arisen to further improve the health and wellbeing of individuals living with type 1 diabetes, allowing many to participate in sport at the local, regional, national or international level of competition. This review and commentary highlights some of the key advances in diabetes management in sport over the last 100 years since the discovery of insulin.

Nutritional Strategies of an Athlete with Type 1 Diabetes Mellitus During a 217-km Ultramarathon

Considering the challenges in meeting the high nutritional demand during ultramarathons, the aim of this study was to analyze the nutritional strategies and glycemic response of an athlete with type 1 diabetes (DM1) during participation in a 217-km ultramarathon. A 36-y-old male athlete who was diagnosed with DM1 15 y earlier was studied during participation in the Brazil 135 ultramarathon. Food consumption and blood glucose were recorded during the race, and nutritional intake was calculated after the race. The athlete completed the race in 51 h 18 min. He consumed a total of 3592 kcal, 532 g carbohydrate, 166 g protein, 92 g lipid, and 14 L of water during the race. Glycemic values ranged from 3.6 to 18.2 mmol·L^-1. Most glycemic values (47%) ranged from 3.9 to 10 mmol·L^-1, whereas 5% were <3.9 mmol·L^-1, 16% were >10 to 13.9 mmol·L^-1, and 32% were >13.9 mmol·L^-1. This case report describes the dietary profile of an athlete with DM1 during a 217-km ultramarathon. Although the athlete implemented strategies that differed from those recommended in the literature, food and nutrient intake and the glycemic management strategy adopted allowed him to successfully finish the race. These results suggest that past personal experiences can be considered and that nutritional recommendations for athletes with DM1 should be individualized.

A Comprehensive Review of Continuous Glucose Monitoring Accuracy during Exercise Periods

Continuous Glucose Monitoring (CGM) has been a springboard of new diabetes management technologies such as integrated sensor-pump systems, the artificial pancreas, and more recently, smart pens. It also allows patients to make better informed decisions compared to a few measurements per day from a glucometer. However, CGM accuracy is reportedly affected during exercise periods, which can impact the effectiveness of CGM-based treatments. In this review, several studies that used CGM during exercise periods are scrutinized. An extensive literature review of clinical trials including exercise and CGM in type 1 diabetes was conducted. The gathered data were critically analysed, especially the Mean Absolute Relative Difference (MARD), as the main metric of glucose accuracy. Most papers did not provide accuracy metrics that differentiated between exercise and rest (non-exercise) periods, which hindered comparative data analysis. Nevertheless, the statistic results confirmed that CGM during exercise periods is less accurate.

In Amateur Athletes With Type 1 Diabetes, a 9-Day Period of Cycling at Moderate-to-Vigorous Intensity Unexpectedly Increased the Time Spent in Hyperglycemia, Which Was Associated With Impairment in Heart Rate Variability

OBJECTIVE

In type 1 diabetes, autonomic dysfunction may occur early as a decrease in heart rate variability (HRV). In populations without diabetes, the positive effects of exercise training on HRV are well-documented. However, exercise in individuals with type 1 diabetes, particularly if strenuous and prolonged, can lead to sharp glycemic variations, which can negatively impact HRV. This study explores the impact of a 9-day cycling tour on HRV in this population, with a focus on exercise-induced glycemic excursions.

RESEARCH DESIGN AND METHODS

Twenty amateur athletes with uncomplicated type 1 diabetes cycled 1,500 km. HRV and glycemic variability were measured by heart rate and continuous glucose monitoring. Linear mixed models were used to test the effects of exercise on HRV, with concomitant glycemic excursions and subject characteristics considered as covariates.

RESULTS

Nighttime HRV tended to decrease with the daily distance traveled. The more time the subjects spent in hyperglycemia, the lower the parasympathetic tone was. This result is striking given that hyperglycemic excursions progressively increased throughout the 9 days of the tour, and to a greater degree on the days a longer distance was traveled, while time spent in hypoglycemia surprisingly decreased. This phenomenon occurred despite no changes in insulin administration and a decrease in carbohydrate intake from snacks.

CONCLUSIONS

In sports enthusiasts with type 1 diabetes, multiday prolonged exercise at moderate-to-vigorous intensity worsened hyperglycemia, with hyperglycemia negatively associated with parasympathetic cardiac tone. Considering the putative deleterious consequences on cardiac risks, future work should focus on understanding and managing exercise-induced hyperglycemia.

Bolus insulin dose depends on previous-day race intensity during 5 days of professional road-cycle racing in athletes with type 1 diabetes: A prospective observational study

AIMS

To assess insulin therapy, macronutrient intake and glycaemia in professional cyclists with type 1 diabetes (T1D) over a 5-day Union Cycliste Internationale road-cycle race.

MATERIAL AND METHODS

In this prospective observational study, seven professional cyclists with T1D (age 28 ± 4 years, body mass index 20.9 ± 0.9 kg/m² , glycated haemoglobin concentration 56 ± 7 mmol/mol [7.3% ± 0.6%]) were monitored during a five-stage professional road cycling race. Real-time continuous glucose monitoring (rtCGM) data, smart insulin pen dose data and macronutrient intake were assessed by means of repeated-measure one-way ANOVA and post hoc testing. Associations between exercise physiological markers and rtCGM data, insulin doses and macronutrient intake were assessed via linear regression modelling (P ≤ 0.05).

RESULTS

Bolus insulin dose was significantly reduced over the 5-day period (P = 0.03), while carbohydrate intake (P = 0.24) and basal insulin doses remained unchanged (P = 0.64). A higher mean previous-day race intensity was associated with a lower mean sensor glucose level (P = 0.03), less time above range level 2 (>13.9 mmol/L [250 mg/dL]; P = 0.05) and lower doses of bolus insulin (P = 0.04) on the subsequent day. No significant associations were found for any other glycaemic range and glycaemic variability (P > 0.05).

CONCLUSIONS

This is the first study to demonstrate the influence of previous-day race intensity on subsequent bolus insulin dose requirements in professional cyclists with T1D. These data may help inform therapeutic strategies to ensure safe exercise performance.

The competitive athlete with type 1 diabetes

Regular exercise is important for health, fitness and longevity in people living with type 1 diabetes, and many individuals seek to train and compete while living with the condition. Muscle, liver and glycogen metabolism can be normal in athletes with diabetes with good overall glucose management, and exercise performance can be facilitated by modifications to insulin dose and nutrition. However, maintaining normal glucose levels during training, travel and competition can be a major challenge for athletes living with type 1 diabetes. Some athletes have low-to-moderate levels of carbohydrate intake during training and rest days but tend to benefit, from both a glucose and performance perspective, from high rates of carbohydrate feeding during long-distance events. This review highlights the unique metabolic responses to various types of exercise in athletes living with type 1 diabetes. Graphical abstract.